Projection devices which enlarge and project an image displayed on, for example, a liquid crystal display onto a screen are well known. There have been various proposals for projection devices which project an image from an oblique direction onto a screen for the purpose of making a more compact projection device while enlarging the screen. This type of oblique projection device is advantageous in that the projection optical system does not block the field of view of the observer since the projection optical system is arranged at a position removed from the center of the screen. However, the oblique projection devices also produce so-called trapezoid distortion in the projection image. There have also been various proposed projection optical systems to correct this trapezoid distortion. For example, Japanese Laid-Open Patent Application Nos. HEI 5-119283 and HEI 5-134213 disclose projection optical systems which are partially eccentric to correct the trapezoid distortion.
The projection optical systems disclosed in Japanese Laid-Open Patent Application Nos. HEI 5-119283 and HEI 5-134213 are not adequately satisfactory from the perspectives of compactness and high performance.